This invention relates to a device for collecting a sample of physiological fluid such as a blood sample so that subsequent analysis may be made for diagnostic purposes. In many such applications, including blood pH and blood gas analysis, it is desirable that the sample be taken in a manner wherein potentially contaminating gases contained in the device are removed while the sample is taken. The present invention incorporates structure to vent unwanted gases and at the same time is configured to be adaptable for use with various analytical laboratory machines in order to avoid the necessity of transferring the sample from one container to another prior to analysis. Accordingly, the sampling device according to the present invention provides a means for selectively isolating a blood sample from contaminant gases.
As noted, the present invention is useful in blood gas analysis and is constructed specifically to enhance the ease and accuracy of this process. The value of blood gas analysis has long been recognized by the medical community, but several problems have been present in utilizing blood gas analysis as a diagnostic tool. Such analysis requires a sample of known volume which is pure from contaminants which would render the results of the analysis suspect. Typical contaminants which often introduce error in analysis are atmospheric air, other gases or fluids, and some solids materials. Isolation of the sample from these contaminants is therefore crucial. Where a blood sample is taken and is subsequently transferred from one container to another prior to analysis, there is an increased chance for introduction of these contaminants. Thus, it is desirable that the analysis take place with the blood remaining in the sampling cartridge.
Another problem that has been confronted in blood gas analysis, which typically requires arterially collected blood, is that the blood cannot be permitted to clot. To this end, prior art devices have preconditioned the container into which the blood sample is received with an anti-coagulant solution although the dilutent of the solution may, itself, cause contamination of the sample. Some prior art techniques include the introduction of crystalline heparin whether as a single crystal or as a crystalline coating on the interior wall of the cartridge so that this problem is alleviated.
The prior art has recognized these problems and has proposed various structures to minimize them. For example, U.S. Pat. No. 4,133,304, issued Jan. 9, 1979 to EMDE Corporation, the assignee of the present invention, discloses an apparatus which permits the collection of a blood sample so that it is isolated within a capillary cartridge of standard volume with this cartridge being coated with a crystalline heparin to prevent clotting of the blood sample. As the sample is drawn into the cartridge through a hypodermic needle, contaminant gases which may be present in the cartridge are vented through the opposite end of the cartridge which is sealed by a resilient member but through which a fiber extends to provide an exhaust passageway for the gas. When the capillary cartridge is filled, the technician removes the fiber so that the resilient seal collapses to seal the blood sample within the cartridge. While this is an exceptionally good device for taking the sample, it has a restriction in that only one sample volume may be obtained so that several different sizes of the sampling device must be produced and stocked to provide versatility of sample volumes.
Another device which uses crystalline heparin is described in U.S. Pat. No. 4,206,768, issued June 10, 1980. This syringe device is similar to a standard hypodermic syringe, having a piston-like sealing member positioned in a cylindrical body and a plunger connected to this sealing member. The only departure of this device from the standard syringe is the provision of a plastic thread which is connected to the plunger and which extends between the wall of the main body of the syringe and the sealing member so as to break the hermetic seal therebetween. This device allows the plunger to be set at a required volume, and, as blood fills the syringe, contaminant gases escape through the broken seal between the side wall of the syringe and the sealing member. When the syringe is filled with blood, the plunger is rotated to withdraw the thread so that a seal may be re-established. Several problems have been noted in this device, however, in that operation requires a fairly complex procedure, including the alignment of the hypodermic needle bevel with the plastic line breaking the seal of the sealing member. An additional problem results in the leakage of blood through the broken seal portion both while the line is in place and after the withdrawal of the plastic line.
Therefore, it is desirable to provide an apparatus which permits the collecting of samples of various selected volumes by a single unit while at the same time isolating the sample from contaminants without leakage. The present device accomplishes this by having a movable sealing member through which contaminant gases may escape but which automatically seals upon contact with a liquid such as blood or other physiological fluid.